1. Field of the Invention
The present invention relates to a method of manufacturing toner, the toner, and a method of recycling the toner.
2. Discussion of the Background
Methods of visualizing image information by forming electrostatic images according to electrophotography are utilized in various kinds of fields now
In the electrophotography, latent images are formed on an image bearing member through the charging and irradiation processes and developed with a development agent containing toner to visualize the images. Thereafter, the visualized images are transferred to and fixed on a recording medium.
The development agent is typified into a two component development agent containing toner and carrier, and a single component development agent in which magnetic toner or non-magnetic toner is singly used. Toner is the main component in both development agents.
Recently, toner having a small particle diameter has been dominant because such toner is advantageous in terms of image quality. Toner is manufactured by a known method such as a dry method using pulverization, an emulsification polymerization agglomeration method, a suspension polymerization method, a drying-in-liquid method, and a phase transfer emulsification method. In pulverization, toner having a desired particle diameter is obtained by: uniformly mixing and dispersing material such as a binder resin, a releasing agent, a coloring agent and an optional charge control agent with a pressure kneader, an extruder, or a medium disperser; pulverizing the mixture by mechanical collision or collision in jet air with a target to obtain toner particles; and classifying the toner particles to obtain toner having a sharp particle size distribution.
The toner for use in electrophotography is typically formed of a binder resin, a coloring agent, and other optional material. Inorganic particulates are externally added and admixed with the toner to improve fluidity of the toner in most cases. Toner to which inorganic particulates are externally added has sufficient fluidity and is suitable to obtain quality images with no white spots.
However, the toner particles and the external additives are agglomerated by heat generation due to high speed stirring and collision of particles in the process of admixing and string toner particles and external additives, which may result in formation of agglomerated toner particles.
In addition, there are problems specific to the wet manufacturing methods, which are agglomerated particles formed in the processes of emulsification, suspension, drying, etc., and coarse particles having a board form ascribable to material fixated on a container or vessel for emulsification, suspension, reaction, etc., and stirring wings, etc.
Such coarse particles tend to have an adverse impact on the image quality. For example, the distance (i.e., the gap) between the photoreceptor and a transfer medium in the transfer process in image formation is caused to be non-uniform by these coarse particles. Also, such coarse particles easily scatter to non-image portions. Furthermore, the difference in the charge of amount among particles arises due to the difference in the particle diameter among particles, which causes uneven image density.
In addition, such coarse toner particles tend to scatter during development and resultantly contaminate inside the image forming apparatus, which leads to degradation of the reliability of the image forming apparatus.
The problem common in the drying method and the wet method is that agglomerated body or coarse toner particles produced in the toner manufacturing process cause production of abnormal images. Thus, methods of removing such agglomerated bodies and/or coarse toner particles in the screening process have been studied and provided.
For example, unexamined published Japanese patent application No. (hereinafter referred to as JOP) 2000-75547 describes a screening process defining the relationship between the temperature of the screen and the temperature of the toner, and the amount of toner supplied to the screen.
JOP 2008-76873 describes a screening method by using a two step screen with definitions for the opening and void ratio thereof.
As described above, various kinds of methods of removing the agglomerated bodies and/or coarse particles formed before the screening process have been studied.
Furthermore, a method of using an ultrasonic screen is used as an economic method of manufacturing toner having a desired particle diameter.
On the other hand, toner is spurred to have a low melting point to deal with full color images and increase the speed of performance. Thus, because of heat generated by ultrasonic vibration to the screen, toner particles easily melt and attach to each other in the screening process, which leads to formation of softly agglomerated particles and commingling thereof into toner products.
Toner having a low melting point that is confirmed to have no agglomerated bodies immediately after the screening process may agglomerate during preservation depending on the preservation condition such as temperature.
Such softly agglomerated toner causes the trouble described above in image formation. Particularly, white spots are formed while having such agglomerated bodies as a core, which results in degradation of the image quality.